r_seneconst

8/3/2019 r_SeneConst

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Photo Essay: How to Build a

Seneca

Plans for this boat may be found at:

http://www.spirainternational.com/

Pacific Power Dory


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To begin building the Seneca, or any

Spira International framed boat, a

strongback jig is required. This is simply

a sturdy beam on which the frames and

other elements of the hulls framing are

set up and temporarily attached to holdthem in position until the adhesive hold-

ing the frame together is cured.

The frames need to be set up on thestrongback, in most cases, higher

than the strongback to establish the

fair curve of the bottom. (Some boats

have a completely flat bottom.) The

blocks need not be as elaborate as

these, but these work very well and

make the following tasks much

easier.

When the frames are set up

on the strongback, it looks

something like this.


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The keelson is

added next to the

frames. Note that

the cutout in the

frames is wider

than the keelson.This is intentional,

to create limber

holes so that bilge

water can move

back and forth

between frames

easily.

Notches in the

frames are cut andthe longitudinal

elements are

added. After the

keelson, the chine

log is the first to be

installed. It runs

the length of the

bottom and side

joint.


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The same procedure used

for the chine log is used

for the sheer clamp, the

longitudinal elementrunning on the top of the

frames. (Actually on the

bottom in this view

beacuse the boat is up-

side down.)

The boats framing is faired, that

is, cut to follow the fair curves of

the side and bottom panels, so that

the plywood planking will have a

nice flat surface to lay against and

get bonded.

The framing itself is used as a

pattern to cut out the plywood. It

diesnt really matter if the bottom

plywood or side plywood is at-

tached first, but it does matter that

whichever is lain first, it must be

accurately trimmed to be flush with

the framing surface so that the next

panel will cover the end grain of

the first.


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Where the plywood meets, butt

blocks made of scrap plywood are

bonded to the inside of the joint,

and screws run through the outer

ply into the butt block to ensure a

secure doubled joint.

You can scarf splice the plywood

together, but it is a lot more work

and not really necessary. These

simple butt-joined panels are

amply strong for anything you

boat is likely to come across.

Here, you can see the meticu-

lous detail this builder used

when creating the plankingjoints on the bow of the boat.

Acheiving this level of crafts-

manship is not difficult, it just

requires patience and atten-

tion to detail.


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Once the planking is

on, the hull starts

looking like it is

really a boat.

Once the epoxy or

polyurethane glue

sets, the hull becomes

rigid and you can

loosen or remove it

from the strongback

jig.

The outside of the

hull is prepped by

filling any counter-

sunk screw holes,

any seams at the butt

blocks, and any other

finsih defects. Pa-

tience here pays off

in the long run.

When this part o fthe hull is complete, most builders elect to cover the hull with

The hull is then flipped

over and removed from the

strongback. The inside is

saturated with epoxy resin.No fiberglass cloth is

needed. The epoxy

strengthens and seals the

wood making the boat both

sturdier and more rot resis-

tant.

fiberglass and epoxy resin.Two layers of 6 oz glass

cloth and epoxy laminating

resin are normally

rcommended.


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Though not spe-

cifically called out

in the plans, this

builder elected to

add an inwale onthe inside of the

frames. This gives

the hull a more

finished appear-

ance.

Strip decking

was added to this

hull. Left bright(varnished,) the

wood appearance

is elegant and

traditional. These

strips are at-

tached directly to

the topside of the

lower frrame

elements.


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Next the various

accessories are

added as desired

by the builder.

Cleats, motor, oarlocks, and in this

case swivel seats.

finish the hull and

make it seaworthy.

Ahhhh... This is what its all about!

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